There is essentially a '2 roll' system currently being used by the game engine when an attack is made at a target.

This page will go over the first roll:

Regarding To-Hit:

The first roll is to determine whether an attack hits or misses it's intended target. The second roll is to determine how much damage is done if the attempt to hit is successful.

Success here takes into consideration things like what level are you compared to what you are attacking, what your skill level with the weapon type you are using it, and the dodge/parry/block skill of the mob you are attacking.

The global chance that an attack will hit is 95%; this is assuming your skill with the weapon you are using is maxed for your level, and that what you are attacking is the same level as you are. For every level the mob is above you there is an increased chance to miss, at the rate of 1% per level for the first few levels. This percentage seems to increase as the level gap increases past single digit level differences.

Note that this 5% chance to miss is not related to block/dodge/parry. This attribute varies with the monster you are attacking, and the Expertise skill is used to counter block/dodge/parry. I will go over this later.

The Hit rating is used to mitigate that 5% chance to miss. At level 80, every 32.79 of hit rating you have means you have reduced the chance to miss by 1%. So if your Hit rating is 33, you only have a 4% chance to miss same level monsters. If your Hit rating is 66(33x2), you only have a 3% chance to miss. If your Hit rating is 165(33 x 5) you have totally overcome the chance to miss and will always hit an even level monster if your weapon skill is maxed for your level.

One of the best visual aids I have seen so far is this table, to represent how these chances for various things to happen really work.

A guildie of ours, Unstopbubble, came up with a table that I think is a great visual aid to understand Hit rating. I am going to put up several of these tables showing how the numbers work based on a player's Crit chance, Hit rating, and Expertise value.

=== === ===

Regarding block/dodge/parry:

All monsters can dodge and parry your attacks. Your expertise rating reduces your chance to be dodged and parried.

Nothing can not block or parry from behind them, only dodge. So melee DPS should always be behind the monster they are fighting where the monster can not parry or block. There is also good reason for this beyond maximizing DPS, some bosses have nasty effects when they parry, so with multiple DPS members hitting a monster from the front it is possible to really have a huge effect on the tank as melee DPS members trigger the parry or block effect repeatedly.

So melee DPS should fight from behind to: A) avoid a chance to be parried or blocked and therefore not do damage with that attack and B) avoid the risk of triggering retaliation from a monster that could adversly effect your tank.

At level 80, every 32.79 expertise = 1% chance to not be dodged or parried. To figure out a definite cap you would need to know the boss's dodge chance, which can vary, but testing tends to point towards a universal rating of 6.5% chance. To negate this, players would need 215 expertise rating to avoid missing due to dodge or parry.

This would be the hit-table for a L80 player fighting a non-elite L80 monster.
A) We will say the monster has nothing special about it.
B) The player has a Crit chance of 20%
C) The player has a Hit Rating of 0.
D) This assumes this monster does of a chance to block, and that the chance is 5%
E) All fractional amounts are rounded up.

---

Base numbers

01 - 05: miss (5%) Standard 5% chance to miss \
06 - 10: parry (5%) Standard 7% chance to parry |> Total 17% chance to miss
11 - 17: dodge (6.5%) Standard 5% chance to dodge/
18 - 80: hit (62%) 100% - 17%(chance to miss) - 20%(chance to crit) = 63%
81 -100: crit (20%) Player's crit-chance 20%

This player will hit this monster 83% of the time with this model.

---

CHANGE:
The player makes sure he/she is attacking from behind the monster. Monsters do not block or parry attacks made behind them.

01 - 05: miss (5%) Standard 5% chance to miss \ Total 12% chance to miss
06 - 12: dodge (6.5%) Standard 7% chance to dodge/
12 - 80: hit (68%) 100% - 12%(chance to miss) - 20%(chance to crit) = 68%
81 -100: crit (20%) Player's crit-chance 20%

This player will hit this monster 88% of the time with this model.

---

CHANGE:
Let's say the player has a Hit rating of 165. (5 x 33) overcoming the 5% chance to miss.

01 - 07: dodge (6.5%) Standard 7% chance to dodge> Only 7% chance to miss now
08 - 80: hit (72%) 100% - 7%(chance to miss) - 20%(chance to crit) = 73%
81 -100: crit (20%) Player's crit-chance 20%

This player will hit this monster 93% of the time now.

---

CHANGE:
Let's now say the player also has an expertise value of 215. (6.5 x 33) overcoming 6.5% chance to dodge.

01 - 80: hit (80%) 100% - 20%(chance to crit) = 80%
81 -100: crit (20%) Player's crit-chance 20%

This player hits the monster 100% of the time.

---

Since I like beating dead horses, lets review quickly:

A) The easiest change a melee DPS person can make for themselves is attacking from behind. You hit 5% more often just for playing smart.

B) Pay attention to your Hit value. The rule of thumb is to climb to an Attack Power of around 2500 first, then look at your armor, weapon, enchantments, and gems, to raise your "to hit" so you don't miss.

C) Once you are 'Hit-Capped' and you're rocking your attack power, it's time to also pay attention to your expertise. Raising it further reduces your chance to miss. This should be worked in as you can, but not reducing your To-Hit or your Attack Power to do so.

Every class has different attributes that add attack power, expertise, and crit chance. My goal is to have that information readily available here, in a form that is clear and understandable. If any of this page is unclear please let me know so I can smooth it out.

---

Now that we are all on the same page of music, lets make things more complicated! YAY!

Elite monsters are effectively 3 levels higher than the level they show up at in your target window. So a level 80 Elite Big-Bad-Scourge-Dude is actually level 83 for purposes of determining your chance to hit it. You can only be level 80 though.

So with a basic 5% chance to miss for even level monsters, and considering that L80 elites are effectively L83, this increases the global chance to miss to 8%. (global 5% + 3 level difference = 8%)

If we do the math, we find we need a Hit Rating of 264(8 x 33) to overcome the 8% chance to miss a L80 Elite monster.